Because divorce or ending a long term commitment is so easy, right?

Easier than letting someone else fuck my partner. Or fucking someone else other than the person I love. YMMV.

You may view nonmonogamy as thinking one person isn’t enough

When did I say or imply that?

someone else may view monogamy as an insecurity-driven way to control your partner

And that IMO, is moronic. Sure, it's true for some cases, but not in the majority. It's generally a values and morals issue, not an insecurity one, that' why I called out the "monogamy=ownership" bit.

There's nothing controlling about wanting monogamous partners or being monogamous yourself, c'mon.

If both partners are okay with one or both getting those needs met outside the relationship, what’s the problem?

If you noticed, I said in another comment that this is logical. If you're ok with that, monogamy doesn't make much sense.